Russian hackers infiltrated voter databases and software systems in 39 states during the 2016 presidential election, an incursion so brazen, it prompted the Obama administration to call Moscow on the hotline to complain, it was reported Tuesday.

The cyberattack targeted software used by poll workers on Election Day, accessed a campaign finance database in at least one state and tried to delete or alter voter data in Illinois, Bloomberg News reported.

The interference in the election process led the Obama White House to use the “red phone,” a direct line between Washington and the Kremlin, to warn that Russia’s action could instigate a broader conflict, Bloomberg reported.

The details of the cyber-assault on the election, some of which were also contained in reporting by the Intercept using leaked classified documents from the National Security Agency, show the extent of Russian meddling and warn of potential weaknesses that could be exploited down the road.

A former senior US official told Bloomberg that Moscow now has three years to build on their knowledge of the voting process before the next presidential election and is confident they will use what they have learned.

Former FBI Director James Comey, testifying last week before the Senate Intelligence Committee, which is investigating Russian interference in the election, warned that the Kremlin “will be back.”

“If they are patriotic, they contribute in a way they think is right, to fight against those who say bad things about Russia,” Putin said.

After the Obama administration complained to Russia about the aggressive intrusions, Moscow asked for more information and said it would investigate the allegations, Bloomberg reported.

“Last year, as we detected intrusions into websites managed by election officials around the country, the administration worked relentlessly to protect our election infrastructure,” Eric Schultz, a spokesman for former President Barack Obama,​ told Bloomberg​. “Given that our election systems are so decentralized, that effort meant working with Democratic and Republican election administrators from all across the country to bolster their cyber-defenses.”